Improved durability of hydrogen storage alloys

An effective and durable hydrogen storage module was required to fuel micro-power systems. Two primary specifications for the hydrogen fuel module in this application were a high volumic storage capacity and rapid hydrogen storage and release under atmospheric pressure or lower at room temperature. In addition, the hydrogen module should be operable for thousands of cycles with fast hydriding and dehydriding rates and be resistant to deactivation on exposure to air for many months and longer. In our prior work, mechanical grinding a small amount of palladium with the hydrogen storage alloys was shown to greatly improve the hydrogen storage performance. The palladium treatment of three intermetallic alloys, AB₅ type LaNi_4.7Al_0.3 and CaNi₅, and A₂B type Mg₂Ni, lowered the activation pressure to sub-atmospheric pressure at room temperature and also significantly increased the hydrogen absorption and desorption rates. This work focused on the durability of hydrogen absorption and desorption performances after exposure of the storage materials to air. The palladium treated hydrogen storage alloys retained both low activation pressures and fast absorption and desorption rates even after more than 2 years air exposure.     

V含量对低钒Ti-V-Cr储氢合金储氢性能的影响

研究了V含量由5at%升高到35at%时,Ti-V-Cr储氢合金组织、相结构及储氢性能的变化.SEM及XRD结果显示:V含量为5at%的Ti-V-Cr合金由Cr1.97Ti1.07相和Cr2Ti相及很少量的Ti相组成;V含量为10at%的Ti-V-Cr合金除了包含前述的3相外还出现了一定量的V基bcc固溶体相;而V含量为35at%的Ti-V-Cr合金转变为以V基bcc固溶体为主相的固溶体储氢合金.随着V含量的升高和组织结构的变化,Ti-V-Cr合金最大吸氢量升高,放氢率也增大,但是吸氢速率显著减小,活化性能变差.室温下,V含量为35at%的合金具有最大的吸氢量并且放氢率也最高,最大储氢量和放氢率分别是2.86%(质量分数)和61%.     

Numerical simulation of hydrogen desorption from high-density metal hydride hydrogen storage vessels

Metal hydride (MH) alloys are a promising type of material in hydrogen storage applications, allowing for low-pressure, high-density storage. However, while many studies are being performed on enhancing the hydrogen storage properties of such alloys, there has been little research on large-scale storage vessels which make use of the alloys. In particular, large-scale, high-density storage devices must make allowances for the temperature variations caused by the heat of reaction between hydrogen and MH alloys, which may impact the storage characteristics. In this study, we propose a numerical model for the design and evaluation of hydrogen storage devices using MH alloys. Hydrogen desorption reaction behavior for an alloy is observed in terms of temperature and reaction rate. This behavioral correlation is used as the basis for a comprehensive simulation model of the alloy system. Calculated results are found to be in good agreement with experimentally measured data, indicating that the model may be applied to multiple system geometries, scales, and alloy compositions.     

Decomposition kinetics of lithium amide for hydrogen storage materials

The kinetic behavior of LiNH₂ decomposition by ammonia release was quantified using thermogravimetric analysis (TGA). While not itself a hydrogen storage material, LiNH₂ is a primary component of the hydrided state in Li–N–H storage materials based on Li₃N or Li₂NH. Its decomposition by ammonia release, and consequent degradation of the hydrogen storage capacity, has important implications for the durability of Li–N–H storage systems. LiNH₂ from two commercial lots and one batch prepared at GM R&D were ball milled for 10 or 20 min to obtain fine LiNH₂ powders. Kinetic parameters were extracted from sets of TGA weight loss curves taken at different heating rates. The activation energy for the decomposition reaction was determined to be about 128 kJ/mole, virtually independent of the source and purity of the LiNH₂, its stoichiometry, ball milling time, and TGA sample size. The reaction rate was found to depend on the sample size as a consequence of the very low NH₃–LiNH₂ equilibrium vapor pressure at temperatures below 300 °C. Larger samples produce a local concentration of NH₃ high enough to inhibit further reaction. Direct isothermal measurements of the initial reaction rates at temperatures between 200 and 300 °C agree well with the values calculated from the heating rate-derived kinetic parameters. The durability of Li–N–H for hydrogen storage was estimated from the measured kinetic parameters by calculating the time required to decompose 20% of the initial LiNH₂, as a function of the operating temperature. The predicted lifetime falls below 10⁵ min for operating temperatures in excess of 160 °C.     

Hydrogen absorption–desorption properties of Ti0.32Cr0.43V0.25 alloy

Ti_0.32Cr_0.43V_0.25 alloy specimens were heat treated, and its various hydrogen storage properties were measured at 303 K to examine its potential as a hydrogen storage material. The heat treatment improved not only the total and the effective hydrogen storage capacities, but also the plateau flatness. The heat of hydride formation was approximately −36 kJ/mol H₂. The effective hydrogen storage capacity remained at approximately 2 wt% after 1000 cycles of pressure swing cyclic tests. The hydrogen storage capacity could be recovered almost to the initial state by reactivating the alloy. The hydrogen absorption rate increased with the repetition of cycling for the first several cycles and remained almost constant afterward. At the 504th cycle, more than 98% of the hydrogen was absorbed within the first 2 min. X-ray diffraction (XRD) patterns showed that the crystal structure of the alloy became more amorphous as the number of cycles increased.     

球磨改性处理对Ti0．9Zr0．1Mn1．5合金相结构及储氢性能的影响

系统研究了Ti0．9Zr0．1Mn1．5储氢合金经不同时间（t=0min，10min，30min，60min）球磨改性处理后对其相结构及储氢性能的影响。结构分析表明，Ti0．9Zr0．1Mn1．5合金在球磨改性处理前后均由单一的六方结构的C14型Laves相组成；随着球磨时间的延长，合金粉的平均粒度减小，并出现了部分团聚现象。储氢性能测试表明，铸态合金经4次吸放氢循环后活化，室温最大吸氢量和有效放氢量分别为209．3ml／g和157．6ml／g，放氢率为75．3％；随着球磨时间的延长，合金的活化性能得到改善，室温最大吸氢量和有效放氢量均先升后降，且都在球磨30min时达到相应最高值231．4ml／g和203．8ml／g，放氢率达到88．1％。由此可见，适当的球磨改性处理能有效地改善Ti0．9Zr0．1Mn1．5合金的综合储氢性能。     

Hydrogen storage alloys for high-pressure suprapure hydrogen compressor

In this work, AB₅ type rare earth-based and AB₂ type TiCr₂-based hydrogen storage alloys were studied for the purpose of high-pressure hydrogen compression. A pair of hydrogen storage alloys, Ml_0.55Mm_0.2Ca_0.25Ni₅ (Ml: La-rich mischmetal; Mm: Ce-rich mischmetal) and (Ti_0.97Zr_0.03)_1.1Cr_1.6Mn_0.4, with favorable hydrogen storage properties was developed as the alloys for a double-stage high-pressure metal hydride hydrogen compressor (MHHC). With the developed alloy pair, we designed and built a MHHC prototype with hydrogen capacity of 100 L, which could produce high-pressure ultrapure hydrogen with pressure of 45 MPa and purity of 99.9999% from industrial grade hydrogen (98% purity) at pressure of around 2 MPa. During the compression procedure, only hot water is used as the heating source. The compression characteristics were studied and the thermal efficiency was calculated.     

金属氢化物氢压缩机用AB2型Ti- Mn基储氢合金研究

制备了AB2型Laves相Ti- Zr- Mn- Cr- V- Fe系列氢压缩材料,对于V- Fe、Mn/Cr比值和Zr含量对合金吸放氢平台特性和热力学性能的影响进行了研究,优化出具有优异综合储氢性能的氢压缩材料Ti0.9Zr0.1Mn1.4Cr0.35V0.2Fe0.05合金.该合金具有较低的吸放氢平台压力、较小的压...     

Oxidation behavior of the (Cu78Y22)98Al2 bulk metallic glass containing Cu5Y-particle composite at 400–600 °C

The oxidation behavior of the (Cu₇₈Y₂₂)₉₈Al₂ bulk metallic glass containing 55% Cu₅Y particles (CYA-composite) was studied over the temperature range of 400–600 °C in dry air. The results generally showed that the oxidation kinetics of the composite obeyed a two-stage parabolic-rate law, with its steady-state parabolic-rate constants (k_p values) increased with temperature. In addition, the oxidation rates of the composite were significantly lower than those of the polycrystalline Cu–20%Y alloy. The scales formed on the composite consisted mostly of hexagonal-Y₂O₃ (h-Y₂O₃) and minor CuO, while significant amounts of Cu₂O and CuO, with minor amounts of Y₂O₃ were detected for the Cu–20%Y alloy. It was found that the absence of Cu₂O is responsible for the slower oxidation rates of CYA-composite.     

The electrochemical hydrogen storage of CNTs synthesized by CVD using LaNi5 alloy particles as catalyst and treated with different temperature in nitrogen

The multi-wall carbon nanotubes (MWNTs) were synthesized by chemical vapor deposition (CVD) using LaNi₅ alloy particles as catalyst. The effect of 40–60 nm MWNTs treated with different temperature in nitrogen on the electrochemical properties of CNTs–Ni electrode were investigated. Three-electrode system was introduced for testing electrochemical hydrogen storage of the electrode. The CNTs–Ni electrodes were used as the working electrode, which were prepared by mixing MWNTs and Ni powder in a weight ratio of 1:10 (MWNTs:Ni). Ni(OH)₂/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode. A 6 mol/L KOH solution acted as the electrolyte. MWNTs treated with different temperature in nitrogen ambient represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition. The CNTs–Ni electrodes with 40–60 nm diameter CNTs which were treated in a temperature of 800 °C in nitrogen has the best electrochemical hydrogen storage capacity of 588.1 mAh/g and a corresponding discharging plateau voltage of 1.18 V. From 500 to 800 °C, the higher temperature the MWNTs treated, the better the electrochemical hydrogen storage property of them is. This shows that the temperature of treatment is an important factor that influences electrochemical hydrogen storage performance of MWNTs.     

Regenerating deuterium absorption of Ti36Zr40Ni20Pd4 icosahedral quasicrystal

Ti/Zr-based icosahedral quasicrystals are a kind of promising hydrogen storage materials, however their absorption regeneration after oxidation-poisoning has been scarcely studied. This work is intended to investigate the deuterium-storage regeneration of a suction-cast Ti₃₆Zr₄₀Ni₂₀Pd₄ quasicrystal. It was found that only through hot vacuuming the quasicrystal could be refreshed from air-flow poisoning to absorb deuterium in two cycles. During the first absorption course, a pregnancy period was observed before the real deuterium uptake while deuterium was loaded rapidly during the second one. The deuterium concentration in the alloy can reach 0.011 mol?D₂/(g?M) (corresponding to a hydrogen mass percent of 2.2%. D₂ and M denote molecular deuterium and the metallic alloy). But the loaded deuterium was very difficult to release completely even by eight-stage desorption at different temperatures. After the second desorption, the quasicrystal phase remained in a small volume, as though the desorption temperature was beyond the crystallization temperature of the quasicrystal. This probably is attributed to the solution function of residual deuterium in the alloy.     

Effect of boron doping on the mechanical properties of ordered Ni–Mo alloys

HASTELLOY B-2 alloy was found to exhibit environmental embrittlement when tested in air and hydrogen at ambient temperature after atomic ordering introduced by a heat treatment at 700 °C for 24 h. Molybdenum in the HASTELLOY B-2 alloy was probably reactive enough to dissociate water vapor in air to generate atomic hydrogen, resulting in hydrogen embrittlement. The percentage of transgranular fracture increased as the test environment changed from hydrogen gas to moist air or water vapor, and vacuum or oxygen. With the addition of 100 wt ppm B, the environmental embrittlement was completely eliminated, with the tensile properties independent of both test environment and strain rate. The fracture mode remained the same, i.e. ductile dimpling, after B-doping when tested in different environments. The immunity of the B-doped B2 alloy to environmental sensitivity remained even after long-term heat treatment. Auger analysis does not detect any boron segregation at the grain boundaries. The mechanism of boron doping in eliminating the environmental embrittlement in the Ni–Mo alloy is apparently different from that in many L1₂-type alloys such as Ni₃Al and Ni₃Si.     

Deuterium Storage of Ti39Zr38Ni17Pd6 Icosahedral Quasi- crystal

Ti-Zr-Ni基二十面体准晶是一类特殊的储氢材料,在氢能和核聚变能领域具有较强应用前景。采用XRD、TEM、XPS技术和气固反应系统研究了Ti39Zr38Ni17Pd6二十面体准晶的储氘性能。该合金室温下的饱和吸氘浓度接近 11 mmol·D2/g·M (D2指氘分子,M指金属),超过Zr2Fe和ZrCo 2种合金。在吸放氘循环过程中,没有发现该合金发生相转变。饱和吸氘使得准晶格膨胀了6.37%,并使得Ti与Zr的结合能上升0.2和0.6 eV,反映出氢原子在这种材料中的占位更靠近这2种金属原子。放氘结果显示该合金具有可能较低的坪台压力,350 ℃左右低于1 kPa,这意味着氘原子在该合金中比在ZrCo合金中具有更高的稳定性。以上结果表明,这种准晶有可能替代Zr2Fe和ZrCo合金而在核聚变能领域得到应用。     

Hydriding properties of La2Mg16Ni alloy prepared by mechanical milling in benzene

The hydrogen storage properties of La₂Mg₁₆Ni alloy prepared by mechanical milling in benzene were investigated. The ball-milling times (0, 5, 10 and 20 h) significantly influence the hydriding process. Compared with the unmilled sample, these as-milled alloys are ready to be activated and the absorption kinetics are relatively fast even at low temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the microstructure and morphology.     

Ti–V–Mn based alloys for hydrogen compression system

Ti–V–Mn based hydrides are one family of alloys with improved hydrogenation properties and they have a great potential to replace the AB₅ alloys as the sorption materials in hydrogen compression systems, although there still are many problems associated with their use, including unstable reversible hydrogen capacity and unfavorable thermodynamic properties. To gain a better understanding on the effect of the substitution elements and to optimize the alloy composition for high storage capacity, the influence of the alloy stoichiometry was investigated. Ti–Zr–V–Mn alloys were prepared by arc melting technique and were annealed in vacuum at temperature above 900 °C to obtain great sorption properties. Hydrogen absorption and desorption kinetics and PCT characteristics of these alloys at ambient temperature were measured and compared. These hydrogen storage features were also discussed in relation to the effect of alloy element compositions. Ti–Zr–V–Mn alloy cycling behavior was also examined.     

Hydrogen storage properties of TiMn2-based alloys

Several TiMn₂-based C14 Laves phase alloys were prepared and their hydrogen storage properties studied in order to develop suitable materials for hydrogen storage tank or hydride heat pump applications. It was observed that the plateau characteristic of the stoichiometric alloy AB, was better than that of the non-stoichiometric one. The plateau pressure was effectively decreased by the partial substitution of Zr for Ti, while the slope was increased. The substitution effects of other transition elements, such as Cr, V, Cu, Fe, Ni for Mn, were also examined. It was found that Cr was suitable for decreasing the hysteresis, Cu could flatten the plateau with decreasing storage capacity, and V could effectively lower the plateau pressure without decreasing the storage capacity. The hydriding properties were found to be related to the lattice structures. Considering a careful balance of the substitution effects of the alloying elements, it was found that Ti_0.85Zr_0.15MnCr_0.8V_0.1Cu_0.1 alloy had very good plateau characteristics with considerably small hysteresis and high storage capacity.     

Hydrogen storage properties of melt-spun LaNi4.25Al0.75

Rapidly solidified LaNi_4.25Al_0.75 alloy was prepared by melt spinning and its hydrogen storage properties were examined. The hydrogen storage capacities and the equilibrium pressures of the unannealed melt-spun (UMS) LaNi_4.25Al_0.75 alloy were found to be nearly identical to those of the annealed induction-melt (AIM) alloy. However, the resistance to pulverization was greatly improved and the hysteresis was markedly decreased for the UMS alloy, while its activation became rather difficult.     

退火热处理对Nd0.75Mg0.25(Ni0.8Co0.2)3.5储氢合金结构和性能的影响

采用中频感应熔炼制备Nd0.75Mg0.25(Ni0.8Co0.2)3.5储氢合金,在0.03 MPa氩气氛围进行退火,退火温度分别为850,900和950 ℃,保温时间均为7 h。分别对合金的电化学性能、气态储氢性能和合金的微观结构进行研究。结果表明,合金在退火热处理前后的相组成没有发生明显变化,主相均为Ce2Ni7型(Nd,Mg)2(Ni,Co)7相和CaCu5型NdNi5相。合金中晶粒尺寸随着退火温度的升高而增大,相界面则减少,退火消除晶格应力、增加成分均匀性、增加储氢容量;同时有部分Mg在热处理过程中损失导致储氢容量的下降。900 ℃热处理使得Nd0.75Mg0.25(Ni0.8Co0.2)3.5合金表现出较好的储氢性能,最大电化学放电容量为359 mAh/g,合金电极在100次循环后容量保持率为90.3%,气态储氢容量达到1.65%（质量分数,下同）。     

Mg-4Zn-2Y合金的高温拉伸流变本构关系

通过对轧制态Mg-4Zn-2Y合金在不同热变形温度以及应变速率下进行高温拉伸试验,研究了Mg-4Zn-2Y合金在不同工艺参数下进行热变形时流变应力的变化规律,并绘制了热加工图。结果表明,流变应力与变形温度以及应变速率均有关系,热变形温度不变时,材料的最大流变应力会随着应变速率的提高而增大;在应变速率不变时,材料的最大流变应力随着变形温度的升高会逐渐下降。采用双曲正弦修正的本构模型确定了轧制态Mg-4Zn-2Y合金的变形激活能Q=242 233.2 J·mol^-1,应力指数n=8.09。通过热加工图确定了Mg-4Zn-2Y合金的可加工区域为472.15~545.00 K,10^-3~10^-4 s^-1和545.00~672.15 K,10^-4~10^-1 s^-1。